Hints on article and category access permissions

Articles have their own access rights. They do not inherit access rights from any parent category.

When you edit a category and change its permissions, you'll get a confirmation window that allows you to set the same access permissions for contents of that category including articles, subcategories, and articles in subcategories.

Access permissions of a category define default permissions for
all new articles created in this category. However they doesn't affect visibility
of existing articles.

When you edit permissions of a group at Users & Groups > Manage Groups, you can change permissions to categories, but it is impossible to change permissions to articles from there.

If you want to hide a category, you have to make it and all its articles restricted.

If there is at least one "public" article in a category, this category (even if it is restricted) will be shown to public.